In many types of rotating rigid disk files, each of the read/write transducers or heads is supported on a carrier (or slider) which rides on a cushion or bearing of air above the surface of the disk when the disk is rotating at its operating speed. The slider is connected to a linear or rotary voice coil actuator by means of a relatively fragile suspension. There is generally a stack of disks and a number of actuators with each actuator supporting a number of sliders. The actuators move the sliders radially between the disk so that each head may access the recording area of a respective disk.
In these conventional disk files the slider is biased against the disk surface by a small force from the suspension when the disk is not rotating. The slider is thus in contact with the disk surface from the time the disk file is turned on until the disk reaches a speed sufficient to cause the slider to ride on the air-bearing. The slider is again in contact with the disk surface when the disk file is turned off and the rotational speed of the disk falls below that necessary to create the air-bearing. In such contact start/stop (CSS) disk files a lubricant is often maintained on the disk surface to prevent damage to the head and the disk during starting and stopping of the disk.
A serious problem with such disk files is that after the slider has been in stationary contact with the disk surface for just a short period of time, the slider tends to resist translational movement or "stick" to the disk surface. This "stiction" is caused by a variety of factors, including static friction and viscous shear forces and surface tension created by the lubricant between the disk and the slider. Even in those disk files which have disks with extremely smooth unlubricated disk surfaces, stiction may occur because of the strong intermolecular attraction at the interface between the smooth disk and slider surfaces. Stiction in a disk file can result in damage to the head or disk when the slider suddenly breaks free from the disk surface when disk rotation is initiated. In addition, because the suspension between the actuator and the slider is relatively fragile in order to permit the slider to fly above the disk surface, sudden rotation of the disk can also damage the suspension.
Thin film metal alloy magnetic recording disks for use in such disk files typically comprise a substrate, such as an aluminum-magnesium (AlMg) alloy disk blank with a nickel-phosphorous (NiP) surface coating, a cobalt-based alloy sputter-deposited as the magnetic layer on the substrate, and a protective overcoat, such as a sputter-deposited amorphous carbon or amorphous hydrogenated carbon film, formed on the magnetic layer. Such disks may also include a sputter-deposited underlayer, such as a layer of chromium (Cr), between the substrate and the magnetic layer. The NiP coating is formed on the AlMg disk blank by electroless deposition from an aqueous solution. The NiP coating covers up imperfections on the AlMg surface and provides hardness in order to minimize any damage to the disk caused by the slider during operation of the disk file.
Prior to the sputter deposition of the cobalt alloy magnetic layer or the Cr layer on the disk substrate, the NiP coating is polished so that the subsequently deposited films, which will conform to the surface topography of the NiP coating, are as smooth as possible. When the disks are of the type for use in CSS disk files, mechanical texturing may also be performed on the NiP surface coating, or at least on the portion of the NiP surface coating where the air-bearing slider will come to rest on the disk. The mechanical texturing is required to minimize the effect of stiction.
What is desired is a disk substrate which has improved properties over those provided by the NiP coating, which is more compatible with the conventional process of sputter deposition of the films making up the magnetic recording disk structure, and which eliminates the need for mechanical texturing.